A Thorough Examination of the Solution Conditions and the Use of Carbon Nanoparticles Made from Commercial Mesquite Charcoal as a Successful Sorbent for Water Remediation

Water pollution has invaded seas, rivers, and tap water worldwide. This work employed commercial Mesquite charcoal as a low-cost precursor for fabricating Mesquite carbon nanoparticles (MUCNPs) using a ball-milling process. The scanning electron energy-dispersive microscopy results for MUCNPs revealed a particle size range of 52.4–75.0 nm. The particles were composed mainly of carbon with trace amounts of aluminum, potassium, calcium, titanium, and zinc. The X-ray diffraction peaks at 26.76 and 43.28 2θ° ascribed to the (002) and (100) planes indicated a crystalized graphite phase. Furthermore, the lack of FT-IR vibrations above 3000 cm−1 showed that the MUCNPs were not functionalized. The MUCNPs’ pore diameter, volume, and surface area were 114.5 Ǻ, 0.363 cm3 g−1, and 113.45 m2 g−1. The batch technique was utilized to investigate MUCNPs’ effectiveness in removing chlorohexidine gluconate (CHDNG) from water, which took 90 min to achieve equilibrium and had an adsorption capacity of 65.8 mg g−1. The adsorption of CHDNG followed pseudo-second-order kinetics, with the rate-limiting step being diffusion in the liquid film. The Langmuir isotherm dominated the CHDNG adsorption on the MUCNPs with a correlation coefficient of 0.99. The thermodynamic studies revealed that CHDNG adsorption onto the MUCNPs was exothermic and favorable, and its spontaneity increased inversely with CHDNG concentration. The ball-milling-made MUCNPs demonstrated consistent efficiency through regeneration–reuse cycles.


Introduction
Water is an essential life for living organisms and hum cal products (PhPs) was disco help to understand the enorm from agricultural areas, and m cant sources of water contam pharmaceutical components (

Introduction
Water is an essential life element, temperature buffering agent, and metabolism media for living organisms and human beings [1]. Knowing that water pollution by pharmaceutical products (PhPs) was discovered in 1960 but was not considered a threat until 1999 may help to understand the enormity of the problem [2,3]. Municipal and sewage waste, runoff from agricultural areas, and machine-washing in pharmaceutical enterprises are all significant sources of water contamination that provide intermediates, raw materials, and active pharmaceutical components (APIs) [4][5][6]. Additionally, transboundary pollution can affect areas thousands of miles from the emergence point, reaching other countries through oceans, and thus, making this a global concern [7][8][9]. Although chronic exposure to PhPs in water is considered a severe public health problem, conventional treatments have not been successful in keeping them out of oceans, rivers, or tap water [10]. Water pollution is considered to be a direct cause of cause for the spread of renal failure, cancers, congenital

Materials
Commercial MSQ charcoal was purchased from a local market in Khartoum, Sudan. UniLab Pharmaceuticals, Mumbai, India, was the source of the CHDNG.

Preparation of MUCNPs Nanoparticles
Five grams of MC were crushed in a porcelain mortar and then moved to a stainlesssteel milling crucible with a capacity of fifty milliliters. Each crucible contained seven stainless steel balls, and the ball-milling equipment was run at 500 RPM for 10.0 h. A powder was generated by sonicating 100 mL of distilled water (DW) for 4 h before being filtered and dried at 120 • C.

Adsorption Studies
The CHDNG Adsorption tests on the MUCNPs were studied via a batch technique. A mixture of 50 mg of MUCNPs and 120 mL of 100 mg L −1 CHDNG was stirred using a magnetic stirrer, and the data collected were utilized in the study of sorption kinetics. Additionally, CHDNG sorption onto MUCNPs was examined, along with the effect of pH within a range of pH 2 to pH 10. Fifty milligrams of SMCNPs were mixed with two hundred milliliters of the adjusted solution and stirred for two hours. Furthermore, sorption experiments were also performed at 20 • C using 25, 50, 75, and 100 mg L −1 of CHDNG concentrations to examine the effect of this variable, and the obtained results were employed in the kinetic investigations. The CHDNG removal from the four serial concentrations was tested within a 20 to 50 • C temperature range in order to study the effect of temperature.

Regeneration Study
Sorbent reusability is an economic factor; therefore, examining this factor is essential. Since the CHDNG is highly soluble in ethanol, the used sorbent was sonicated with 10 mL ethanol for 15.0 min, filtered, rinsed with another 10 mL ethanol, and dried at 120 • C for two hours.

Characterizations
The SEM examination was used to analyze the morphology of the MUCNPs' surfaces. Figure 1a shows the SMCNPs SEM results, which possessed particles of sizes ranging from 52.4 to 75.0 nm. Additionally, the EDX was utilized to examine the elemental composition of the MUCNPs (Figure 1b,c). The commercial MC was composed mainly of carbon (86.0%) and trace amounts of aluminum, potassium, calcium, titanium, and zinc.
The MUCNPs' crystallinity and phase purity were tested via the XRD (Figure 2a). The data obtained showed that there were diffraction peaks at 26.76 and 43.28 2-theta degrees that can be ascribed to the (002) and (100) planes of a cubical-lattice graphite phase [47]. The complexity of the XRD spectrum can be explained by the multi-element composition of the commercial muskat charcoal revealed by the EDX. The MUCNPs' crystallinity and phase purity were tested via the XRD (Figure 2a). The data obtained showed that there were diffraction peaks at 26.76 and 43.28 2-theta degrees that can be ascribed to the (002) and (100) planes of a cubical-lattice graphite phase [47]. The complexity of the XRD spectrum can be explained by the multi-element composition of the commercial muskat charcoal revealed by the EDX.
Moreover, FTIR spectrophotometry was employed to survey the functional groups of the fabricated MUCNPs (Figure 2b). The results of MUCNPs revealed vibration peaks from 400 to 900 cm −1 corresponding to the metal oxides revealed by EDX. The bands at 1429, 1590, and 1708 cm −1 can be assigned to the MUCNPs' carbon skeleton. Additionally, the absence of vibrations above 3000 cm −1 implied that the MUCNPs were not functionalized. Moreover, FTIR spectrophotometry was employed to survey the functional groups of the fabricated MUCNPs ( Figure 2b). The results of MUCNPs revealed vibration peaks from 400 to 900 cm −1 corresponding to the metal oxides revealed by EDX. The bands at 1429, 1590, and 1708 cm −1 can be assigned to the MUCNPs' carbon skeleton. Additionally, the absence of vibrations above 3000 cm −1 implied that the MUCNPs were not functionalized.
The N 2 adsorption-desorption technique was used to study the surface properties of MUCNPs (Figure 2c The N2 adsorption-desorption technique was used to study the surface properties of MUCNPs (Figure 2c,d). The MUCNPs have an H3 hysteresis loop, typical of cylindricalpored mesoporous materials [48][49][50]. The Brunauer-Emmett-Teller (BET) method was selected to compute the MUCNPs' surface area (SA), and the Barrett-Joyner-Halenda (BJH) method was chosen to estimate the MUCNPs' pore diameter and volume (PD and PV). The MUCNPs possessed PD = 114.5 Ǻ , PV = 0.363 cm 3 g −1 , and SA = 113.45 m 2 g −1 .  Figure 3a depicts the contact time influence on CHDNG removal by MUCNPs. The removal trend progressed up to 90 min (equilibrium time), and the obtained experimental qt value was 65.8 mg g −1 . The temperature and initial feeding concentration are crucial factors affecting the adsorption process. Figure 3b demonstrates the proportionality of the resulting qt and feeding concentration. In conclusion, a higher starting concentration has the potential to provide a powerful force that aids in the dispersal of contaminants. However, increasing the solution temperature decreased the CHDN elimination rate (exothermic sorption) [51]. In addition, the qt correlated positively with feed concentrations, suggesting that a 2:1 sorbent mass-to-solution ratio would be appropriate for the concentrations explored in this study. These results were comparable to current CMs in the literature regarding rapid absorption, short equilibrium duration, and high experimental qt values [52][53][54][55][56]. Notably, the high qt from 100 mg L −1 CHDNG suggested the potential utility of SMCNPs in treating contaminants in significant concentrations. However, the fact that they could remove almost half of the amounts at 25 mg L −1 suggests they could be used effectively in water treatment systems where low quantities are predicted [57]. The concentration and temperature impacts on CHDNG removal through MUCNPs were investigated (Figure 3b).  Figure 3a depicts the contact time influence on CHDNG removal by MUCNPs. The removal trend progressed up to 90 min (equilibrium time), and the obtained experimental q t value was 65.8 mg g −1 . The temperature and initial feeding concentration are crucial factors affecting the adsorption process. Figure 3b demonstrates the proportionality of the resulting q t and feeding concentration. In conclusion, a higher starting concentration has the potential to provide a powerful force that aids in the dispersal of contaminants. However, increasing the solution temperature decreased the CHDN elimination rate (exothermic sorption) [51]. In addition, the qt correlated positively with feed concentrations, suggesting that a 2:1 sorbent mass-to-solution ratio would be appropriate for the concentrations explored in this study. These results were comparable to current CMs in the literature regarding rapid absorption, short equilibrium duration, and high experimental q t values [52][53][54][55][56]. Notably, the high qt from 100 mg L −1 CHDNG suggested the potential utility of SMCNPs in treating contaminants in significant concentrations. However, the fact that they could remove almost half of the amounts at 25 mg L −1 suggests they could be used effectively in water treatment systems where low quantities are predicted [57]. The concentration and temperature impacts on CHDNG removal through MUCNPs were investigated (Figure 3b). The inversed proportionality between temperature and CHDNG removal implied exothermic sorption [58]. The adsorption of CHDNG was studied, and its sensitivity to pH was determined (Figure 3b). The q t data indicated that pH 7.0 was best for CHDNG sorption onto the MUCNPs. The CHDNG's electron-rich sites may become protonated in low pH conditions. However, in an alkaline environment, the hydroxyl groups may deprotonate the CHDNG's acidic sites and/or compete with the pollutants for the adsorption sites [59].

Adsorption of CHDNG
The inversed proportionality between temperature and CHDNG removal implied exothermic sorption [58]. The adsorption of CHDNG was studied, and its sensitivity to pH was determined (Figure 3b). The qt data indicated that pH 7.0 was best for CHDNG sorption onto the MUCNPs. The CHDNG's electron-rich sites may become protonated in low pH conditions. However, in an alkaline environment, the hydroxyl groups may deprotonate the CHDNG's acidic sites and/or compete with the pollutants for the adsorption sites [59].

Kinetics
Equation (1) was used to determine the adsorption capacity, expressed as the milligrams of CHDNG that may be adsorbed onto one gram of MUCNPs (qt, in mg g −1 ). In order to investigate the adsorption rate, the pseudo-first-order (PF) and pseudo-secondorder (PS) kinetic models (Equations (2) and (3)) were utilized. Furthermore, the liquidfilm diffusion model (LD, Equation (4)) and the intraparticle diffusion model (ID, Equation (5)) were used in order to investigate the adsorption step that is present in adsorption [60,61].
The equilibrium adsorption capacity is denoted by qe (mg.g −1 ), while the PF, PS, ID, and LD constants are represented by k1(min −1 ), k2(g mg −1 min −1 ), kIP (mg g −1 min −1/2 ), and kLF (min −1 ), respectively. The Ci (mg g −1 ) was the boundary layer factor [62]. The linear PF and PS plots for the elimination of CHDNG by MUCNPs are shown in Figure 4a,b. CHDNG adsorption on MUCNPs followed the PF kinetic model, with the LD mechanism influencing its sorption on MUCNPs (see Table 1). (Figure 4c,d). These findings supported the PF agreement that CHDNG adsorption depends primarily on migration from the solution to the MUCNP surface. However, the exceptionally high Ci value suggested that ID did not significantly regulate CHDNG sorption on MUCNPs [63]. The sorbent performance is excellent

Kinetics
Equation (1) was used to determine the adsorption capacity, expressed as the milligrams of CHDNG that may be adsorbed onto one gram of MUCNPs (qt, in mg g −1 ). In order to investigate the adsorption rate, the pseudo-first-order (PF) and pseudo-secondorder (PS) kinetic models (Equations (2) and (3)) were utilized. Furthermore, the liquid-film diffusion model (LD, Equation (4)) and the intraparticle diffusion model (ID, Equation (5)) were used in order to investigate the adsorption step that is present in adsorption [60,61].
ln q e − q t = ln q e − k 1 · t (2) The equilibrium adsorption capacity is denoted by q e (mg g −1 ), while the PF, PS, ID, and LD constants are represented by k 1 (min −1 ), k 2 (g mg −1 min −1 ), k IP (mg g −1 min −1/2 ), and k LF (min −1 ), respectively. The C i (mg g −1 ) was the boundary layer factor [62]. The linear PF and PS plots for the elimination of CHDNG by MUCNPs are shown in Figure 4a,b. CHDNG adsorption on MUCNPs followed the PF kinetic model, with the LD mechanism influencing its sorption on MUCNPs (see Table 1). (Figure 4c,d). These findings supported the PF agreement that CHDNG adsorption depends primarily on migration from the solution to the MUCNP surface. However, the exceptionally high Ci value suggested that ID did not significantly regulate CHDNG sorption on MUCNPs [63]. The sorbent performance is excellent considering the CHDNG's short uptake time onto MUCNPs and the experimental q t value (     HF-functionalized activated carbon 24.0 [67] HCl-functionalized activated carbon 23.5 [68] Granular activated carbon 17.5 [69] Nanomaterials 2023, 13, 1485 8 of 13

Sorption Isotherms
The impact of CHDNG concentration on its removal by MUCNPs was investigated (Figure 5a). The experimental q t increased proportionally as the feeding concentration increased, indicating that a 1:2 sorbent-to-solution ratio can effectively treat a 100 mg L −1 CHDNG pollution [59]. These obtained results implied the applicability of MUCNPs to remediate industrial wastewater and contaminated water resources. Further, the results of sorption equilibria from different CHDNG concentrations were utilized for the adsorption isotherm investigations. The adsorption isotherms have been studied using the Langmuir (LM, Equation (6)) and Freundlich (FM, Equation (7)) as the most widely applied isotherm models. 1 ln q e = ln K F + 1 n ln C e The LM and FM were K L (L mg −1 ) and K F (L mg −1 ). Ce (mg L −1 ) is the CHDNG equilibrium concentration, Q m (mg g −1 ) is the maximum q t , and n (arbitrary) is the Freundlich-heterogeneity factor.

Sorption Thermodynamics
The influence of medium temperature on the CHDNG adsorption was explored using different concentrations. Figure 5a revealed a reverse proportionality between qt and tem-   Table 3. Removing CHDNG through MUCNPs functioned better using LM, and the 1/n value being more than unity indicated the unfavorability of multilayer sorption (Table 3) [70][71][72][73].

Sorption Thermodynamics
The influence of medium temperature on the CHDNG adsorption was explored using different concentrations. Figure 5a revealed a reverse proportionality between qt and temperature, which implied exothermic sorption. Furthermore, the temperature impact results were employed to analyze sorption thermodynamics (Figure 5d). The entropy (∆S • ) and enthalpy (∆H • ) were determined using Equation (8), and then the Gibbs free energy (∆G • ) was computed using their values in Equation (9). The resulting values are tabulated in Table 3.
Exothermic sorption was predicted by the negative ∆H • values within the tested concentrations ( Table 3). The negative sign of ∆S • values may indicate the spontaneity of CHDNG removal through MUCNPs. Additionally, the decrease in ∆G • values inversely with temperature corroborates the exothermic discovery of this sorption [74][75][76][77]. The use of this sorbent for water treatment is encouraged by the inverse proportionately of ∆G • with the concentration. Additionally, the ∆H • values of less than 80 kJ mol −1 can be used to forecast the physisorption nature of this process.

Regeneration-Reuse Investigations
The MUCNPs sorbent was regenerated in four consecutive batches. The efficiency of the regenerated MUCNPs was examined by mixing 50 mg of sorbent with 120 mL CHDNG solution ( Figure 6). The MUCNPs showed an average removal percentage of 97.4% during the four cycles with an RSD of 2.6%. The excellent performance of regenerated MUCNPs can be attributed to the nature of the physisorption, with the sorption being controlled by LD and the one-layer sorption trend (LM).

Regeneration-Reuse Investigations
The MUCNPs sorbent was regenerated in four consecutive batches. The efficiency of the regenerated MUCNPs was examined by mixing 50 mg of sorbent with 120 mL CHDNG solution (Figure 6). The MUCNPs showed an average removal percentage of 97.4% during the four cycles with an RSD of 2.6%. The excellent performance of regenerated MUCNPs can be attributed to the nature of the physisorption, with the sorption being controlled by LD and the one-layer sorption trend (LM).

Conclusions
Commercial MSQ charcoal was employed as a low-cost precursor for fabricating MUCNPs via a ball-milling process. SEM-EDX, FTIR, BET, and XRD were utilized to characterize the produced MUCNPs. The batch protocol was employed to study the removal of CHDNG from water. The removal process progressed for one and a half hours, after which there was no significant progress, and a qt of 65.8 mg g −1 was attained. The kinetic investigations showed that the CHDNG adsorption followed the PS kinetic model, and LD influenced CHDNG adsorptions onto MUCNPs. The CHDNG adsorption on the MUCNPs fitted the LM with a correlation coefficient of 0.99. The ball-milling-made MUCNPs performed excellently in removing CHDNG during the regeneration-reuse cycles.

Data Availability Statement:
All data is available under reasonable request from the corresponding author.

Conflicts of Interest:
The authors declare no conflict of interest.

Conclusions
Commercial MSQ charcoal was employed as a low-cost precursor for fabricating MUCNPs via a ball-milling process. SEM-EDX, FTIR, BET, and XRD were utilized to characterize the produced MUCNPs. The batch protocol was employed to study the removal of CHDNG from water. The removal process progressed for one and a half hours, after which there was no significant progress, and a q t of 65.8 mg g −1 was attained. The kinetic investigations showed that the CHDNG adsorption followed the PS kinetic model, and LD influenced CHDNG adsorptions onto MUCNPs. The CHDNG adsorption on the MUCNPs fitted the LM with a correlation coefficient of 0.99. The ball-millingmade MUCNPs performed excellently in removing CHDNG during the regenerationreuse cycles.